Bidirectional power conversion

ABSTRACT

A power conversion apparatus includes: matrix converter circuitry configured to perform bidirectional power conversion between a primary side and a secondary side; and control circuitry configured to: select a first control mode in response to determining that a command-primary frequency difference between a command frequency and a primary side frequency of the matrix converter circuitry is above a predetermined threshold, wherein the first control mode includes causing a secondary side frequency of the matrix converter circuitry to follow the command frequency; select a second control mode in response to determining that the command-primary frequency difference is below the threshold, wherein the second control mode includes maintaining a primary-secondary phase difference between a secondary side phase and a primary side phase of the matrix converter circuitry within a predetermined target range; and control the matrix converter circuitry in accordance with a selection of the first control mode or the second control mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2020-146154, filed on Aug. 31, 2020, theentire contents of which are incorporated herein by reference.

BACKGROUND Field

The present disclosure relates to a power conversion apparatus and apower conversion method.

Description of the Related Art

Japanese Unexamined Patent Application Publication No. 2015-82949discloses a matrix converter in which, when the difference between thefrequency of the output voltage from a power conversion unit to a loadand the frequency of an AC power supply falls within a predeterminedrange, the power conversion unit performs a voltage increase control toincrease the output voltage and a follow-up control to cause the phaseof the output voltage to follow the voltage phase of the AC powersupply, and, after finishing these controls, the power conversion unitconnects the AC power supply directly to the load.

SUMMARY

Disclosed herein is a power converter for matrix converter circuitry.The power conversion apparatus according to an aspect of the disclosuremay include: matrix converter circuitry configured to performbidirectional power conversion between a primary side and a secondaryside; and control circuitry configured to: select a first control modein response to determining that a command-primary frequency differencebetween a command frequency and a primary side frequency of the matrixconverter circuitry is above a predetermined threshold, wherein thefirst control mode includes causing a secondary side frequency of thematrix converter circuitry to follow the command frequency; select asecond control mode in response to determining that the command-primaryfrequency difference is below the threshold, wherein the second controlmode includes maintaining a primary-secondary phase difference between asecondary side phase and a primary side phase of the matrix convertercircuitry within a predetermined target range; and control the matrixconverter circuitry in accordance with a selection of the first controlmode or the second control mode.

A matrix converter circuitry may be configured to perform bidirectionalpower conversion between primary side power and secondary side power. Apower conversion method disclosed herein may include: selecting a firstcontrol mode in response to determining that a command-primary frequencydifference between a command frequency and a primary side frequency ofthe matrix converter circuitry is above a predetermined threshold,wherein the first control mode includes causing a secondary sidefrequency of a matrix converter circuitry to follow the commandfrequency; selecting a second control mode in response to determiningthat the command-primary frequency difference is below the threshold,wherein the second control mode includes maintaining a primary-secondaryphase difference between a secondary side phase and a primary side phaseof the matrix converter circuitry within a predetermined target range;and controlling the matrix converter circuitry in accordance with aselection of the first control mode or the second control mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the configuration of anexample power conversion apparatus.

FIG. 2 is a schematic diagram illustrating an example of a bidirectionalswitch.

FIG. 3 is a graph illustrating transitions of a primary side voltage anda secondary side current.

FIG. 4 is a block diagram illustrating an example configuration of afirst mode control unit.

FIG. 5 is a block diagram illustrating an example configuration of asecond mode control unit.

FIG. 6 is a block diagram illustrating an example configuration of adeterioration detection unit.

FIG. 7 is a graph illustrating an example coefficient profile.

FIG. 8 is a graph illustrating an example degradation profile.

FIG. 9 is a block diagram illustrating an example hardware configurationof control circuitry.

FIG. 10 is a flowchart illustrating an example control mode switchingprocedure.

FIG. 11 is a flowchart illustrating a first mode control procedure.

FIG. 12 is a flowchart illustrating a second mode control procedure.

FIG. 13 is a flowchart illustrating an example phase tracking controlprocedure.

FIG. 14 is a flowchart illustrating an example degradation detectionprocedure.

DETAILED DESCRIPTION

In the following description, with reference to the drawings, the samereference numbers are assigned to the same components or to similarcomponents having the same function, and overlapping description isomitted.

Power Conversion Apparatus

A power conversion apparatus 1 illustrated in FIG. 1 is a device thatperforms bidirectional power conversion between a primary side and asecondary side. For example, the power conversion apparatus 1 convertsthe primary side power supplied from a power supply 91 into thesecondary side power and supplies the secondary side power to anelectric device 92. The power conversion apparatus 1 converts thesecondary side power (regenerative power) generated by the electricdevice 92 into the primary side power and supplies the primary sidepower to the power supply 91.

The primary side power and the secondary side power may be single-phaseAC power or three phase AC power. The primary side power and thesecondary side power may be DC power. Hereinafter, a case where theprimary side power and the secondary side power are both three phase ACpower will be described. For example, the primary side power includesthree phases of an R phase, an S phase, and a T phase, and the secondaryside power includes three phases of a U phase, a V phase, and a W phase.

The power conversion apparatus 1 includes matrix converter circuitry 10,a filter 30, a voltage detection circuit 40, a current sensor 50, and acontrol circuitry 100. Hereinafter, the configuration of each elementwill be described in detail.

Matrix Converter Circuitry

The matrix converter circuitry 10 has a plurality of switching elements,and performs bidirectional power conversion between the primary sidepower and the secondary side power without going through a DC conversionprocess. For example, the matrix converter circuitry 10 has power lines11R, 11S, 11T on the primary side, power lines 12U, 12V, 12W on thesecondary side, and nine sets of bidirectional switches 2RU, 2SU, 2TU,2RV, 2SV, 2TV, 2RW, 2SW, 2TW. A power line 11R is an R phase powertransmission line, a power line 11S is an S phase power transmissionline, and a power line 11T is a T phase power transmission line. A powerline 12U is a U phase power transmission line, a power line 12V is a Vphase power transmission line, and a power line 12W is a W phase powertransmission line.

Each of the bidirectional switches 2RU, 2SU, 2TU, 2RV, 2SV, 2TV, 2RW,2SW, 2TW switches among 3 states: a state in which a current flows fromthe primary side to the secondary side, a state in which a current flowsfrom the secondary side to the primary side, and a state in which nocurrent flows.

A bidirectional switch 2RU is interposed between the power line 11R andthe power line 12U, and switches between a first ON state in which acurrent flows from the power line 11R to the power line 12U, a second ONstate in which a current flows from the power line 12U to the power line11R, and a bidirectional OFF state in which no current flows. Abidirectional switch 2SU is interposed between the power line 11S andthe power line 12U, and switches between a first ON state in which acurrent flows from the power line 11S to the power line 12U, a second ONstate in which a current flows from the power line 12U to the power line11S, and a bidirectional OFF state in which no current flows. Abidirectional switch 2TU is interposed between the power line 11T andthe power line 12U, and switches between a first ON state in which acurrent flows from the power line 11T to the power line 12U, a second ONstate in which a current flows from the power line 12U to the power line11T, and a bidirectional OFF state in which no current flows.

A bidirectional switch 2RV is interposed between the power line 11R andthe power line 12V, and switches between a first ON state in which acurrent flows from the power line 11R to the power line 12V, a second ONstate in which a current flows from the power line 12V to the power line11R, and a bidirectional OFF state in which no current flows. Abidirectional switch 2SV is interposed between the power line 11S andthe power line 12V, and switches between a first ON state in which acurrent flows from the power line 11S to the power line 12V, a second ONstate in which a current flows from the power line 12V to the power line11S, and a bidirectional OFF state in which no current flows. Abidirectional switch 2TV is interposed between the power line 11T andthe power line 12V, and switches between a first ON state in which acurrent flows from the power line 11T to the power line 12V, a second ONstate in which a current flows from the power line 12V to the power line11T, and a bidirectional OFF state in which no current flows.

A bidirectional switch 2RW is interposed between the power line 11R andthe power line 12W, and switches between a first ON state in which acurrent flows from the power line 11R to the power line 12W, a second ONstate in which a current flows from the power line 12W to the power line11R, and a bidirectional OFF state in which no current flows. Abidirectional switch 2SW is interposed between the power line 11S andthe power line 12W, and switches between a first ON state in which acurrent flows from the power line 11S to the power line 12W, a second ONstate in which a current flows from the power line 12W to the power line11S, and a bidirectional OFF state in which no current flows. Abidirectional switch 2TW is interposed between the power line 11T andthe power line 12W, and switches between a first ON state in which acurrent flows from the power line 11T to the power line 12W, a second ONstate in which a current flows from the power line 12W to the power line11T, and a bidirectional OFF state in which no current flows.

As illustrated in FIG. 2, each of the bidirectional switches 2RU, 2SU,2TU, 2RV, 2SV, 2TV, 2RW, 2SW, 2TW comprises two switches 21 and 22. Inan ON state, the switch 21 passes a current from the primary side to thesecondary side without passing a current from the secondary side to theprimary side. In an ON state, the switch 22 passes a current from thesecondary side to the primary side without passing a current from theprimary side to the secondary side. Further, the switches 21, 22 areswitches having a reverse blocking capability capable of maintaining theOFF state in the OFF state with respect to the voltage application inthe direction opposite to the flow direction of the ON state.

The bidirectional switches 2RU, 2SU, 2TU, 2RV, 2SV, 2TV, 2RW, 2SW, 2TWare, for example, in the first on state by turning on the switch 21 andturning off the switch 22, the second on state by turning off the switch21 and turning on the switch 22, and the bidirectional off state byturning off the switches 21 and 22. In FIG. 2, the bidirectionalswitches 2RU, 2SU, 2TU, 2RV, 2SV, 2TV, 2RW, 2SW, 2TW may include diodeseach of which is connected in series with each of the switches 2 land 22having no reverse blocking capability. In some examples, a connectionpoint between the switch 21 and the diode may be connected to aconnection point between the switch 22 and the diode.

Returning to FIG. 1, the filter 30 reduces harmonic components of thevoltage or current on its primary side. For example, the filter 30includes inductors 31R, 31S, 31T and capacitors 34R, 34S, 34T. Theinductors 31R, 31S, 31T are respectively provided in the power lines11R, 11S, 11T. The capacitor 34R is provided between the power line 11Rand a neutral point 35 on the secondary side of the inductor 31R(between the inductor 31R and the bidirectional switches 2RU, 2RV, 2RW).The capacitor 34S is provided between the power line 11S and the neutralpoint 35 on the second order side of the inductor 31S (between theinductor 31S and the bidirectional switches 2SU, 2SV, 2SW). Thecapacitor 34T is provided between the power line 11T and the neutralpoint 35 on the second order side of the inductor 31T (between theinductor 31T and the bidirectional switches 2TU, 2TV, 2TW). As describedabove, since the filter 30 is provided between the power supply 91 andthe matrix converter circuitry 10, the harmonic components of thevoltage or current of the power supply 91 are reduced by the filter 30.

The voltage detection circuit 40 (a voltage sensor) detects aninstantaneous value of the voltage on the primary side of the matrixconverter circuitry 10. For example, the voltage detection circuit 40detects an instantaneous value of the phase voltage of each primary sideof the filter 30. The voltage detection circuit 40 may detect aninstantaneous value of a phase voltage on the secondary side of thefilter 30. Hereinafter, the voltage on the primary side of the matrixconverter circuitry 10 is referred to as “a primary side voltage”. Thecurrent on the primary side of the matrix converter circuitry 10 isreferred to as “a primary side current”.

The current sensor 50 detects the instantaneous value of the current onthe secondary side of the matrix converter circuitry 10 (the currentflowing between the matrix converter circuitry 10 and the electricdevice 92). For example, the current sensor 50 detects the instantaneousvalue of the current in the power lines 12U, 12V, 12W. Hereinafter, thecurrent on the secondary side of the matrix converter circuitry 10 isreferred to as “a secondary side current”. The voltage on the secondaryside of the matrix converter circuitry 10 is referred to as “a secondaryside voltage”. The current sensor 50 may be configured to detect thesecondary side current value of all phases of the power lines 12U, 12V,12W, or may be configured to detect the secondary side current value ofany two phases of the power lines 12U, 12V, 12W. As long as the zerophase current is not generated, the sum of a current values of the Uphase, the V phase, and the W phase is zero, and thus information of thesecondary side current values of all phases is obtained even when thesecondary side current value of two phases is detected.

Control Circuitry

The control circuitry 100 controls the matrix converter circuitry 10 toperform power conversion between the primary side power and thesecondary side power. If a state in which a secondary side phase and aprimary side phase are aligned is maintained in the matrix convertercircuitry 10, current is concentrated on any of the switching elementsof the matrix converter circuitry 10, and heat generation in theswitching element increases. The state in which the secondary side phaseand the primary side phase are aligned corresponds to a state in whichthere is no difference between the primary side phase and the secondaryside phase. In addition, as a secondary side frequency approaches aprimary side frequency, this phenomenon repeatedly occurs at a frequencyof a difference between the secondary side frequency and the primaryside frequency.

On the other hand, the control circuitry 100 is configured to: select afirst control mode in response to determining that a command-primaryfrequency difference between a command frequency and a primary sidefrequency of the matrix converter circuitry 10 is above a predeterminedthreshold, wherein the first control mode includes causing a secondaryside frequency of the matrix converter circuitry 10 to follow thecommand frequency; select a second control mode in response todetermining that the command-primary frequency difference is below thethreshold, wherein the second control mode includes maintaining aprimary-secondary phase difference between a secondary side phase and aprimary side phase of the matrix converter circuitry 10 within apredetermined target range; and control the matrix converter circuitry10 in accordance with a selection of the first control mode or thesecond control mode. For example, the control circuitry 100 isconfigured to perform: a first mode control that includes causing asecondary side frequency of a matrix converter circuitry 10 to follow acommand frequency by the matrix converter circuitry 10 performingbidirectional power conversion between primary side power and secondaryside power; a second mode control that includes maintaining, by thematrix converter circuitry 10, a difference between a secondary sidephase and a primary side phase of the matrix converter circuitry 10 atodd multiples of 60°±30°; and a mode switching that includes switchingthe first mode control and the second mode control so that the firstmode control is performed if the command-primary frequency difference isabove the threshold, and the second mode control is performed if thecommand-primary frequency difference is below the threshold. As aresult, a state in which the secondary side phase and the primary sidephase are aligned is avoided, and thus heat generation of the switchingelement is suppressed. It should be noted that the difference fallingbelow a predetermined threshold means that the magnitude (absolutevalue) of the difference falls below the predetermined thresholdregardless of whether the difference is a positive value or a negativevalue. Similarly, the difference exceeding the predetermined thresholdmeans that the magnitude of the difference exceeds the predeterminedthreshold. The same applies to the following description.

For example, the control circuitry 100 has a phase/amplitude calculationunit 111, a power conversion control unit 112, a current informationacquisition unit 113, a first mode control unit 114, a second modecontrol unit 115, a mode switching unit 116, and a deteriorationdetection unit 117 as a functional configuration (hereinafter referredto as “a functional block”).

The phase/amplitude calculation unit 111 calculates the phase, theoscillation amplitude and the frequency of the primary side voltagebased on the phase voltage of the power lines 11R, 11S, 11T obtained bythe voltage detection circuit 40. Hereinafter, the calculation resultsof the phase, the oscillation amplitude, and the frequency are referredto as “information of the primary side voltage”.

The power conversion control unit 112 switches ON/OFF of thebidirectional switches 2RU, 2SU, 2TU, 2RV, 25V, 2TV, 2RW, 2SW, 2TW inconjunction with a carrier wave so as to output an AC voltage or an ACcurrent corresponding to the control command to the secondary side ofthe matrix converter circuitry 10. For example, based on the primaryside voltage information and the voltage command, the power conversioncontrol unit 112 switches ON/OFF of the bidirectional switches 2RU, 2SU,2TU, 2RV, 25V, 2TV, 2RW, 2SW, 2TW in conjunction with the carrier waveso as to output the secondary side voltage corresponding to the voltagecommand.

More particularly, the power conversion control unit 112 sequentiallyselects each of the R phase, the S phase and the T phase as a referencephase based on the primary side voltage information, and controls thematrix converter circuitry 10 to output the secondary side voltagecorresponding to the voltage command according to the potentialdifferences between the reference phase and the other two phases. Forexample, the power conversion control unit 112 repeats, at the frequencyof the primary side voltage, setting the R phase as a positive referencephase in a first section in which the voltage of the R phase is maximum,setting the T phase as a negative reference phase in a second section inwhich the voltage of the T phase is minimum, setting the S phase as thepositive reference phase in a third section in which the voltage of theS phase is maximum, setting the R phase as the negative reference phasein a fourth section in which the voltage of the R phase is minimum,setting the T phase as the positive reference phase in a fifth section,and setting the S phase as the negative reference phase in a sixthsection.

The power conversion control unit 112 maintains a state in which thereference phase is connected to the secondary side and at the same time,switches ON/OFF between the other two phases and the secondary side. Forexample, in the first section, the power conversion control unit 112switches bidirectional switches 2SU, 2TU, 2SV, 2TV, 2SW, 2TW on and offwhile keeping any of the bidirectional switches 2RU, 2RV, 2RW on. In thesecond section, the power conversion control unit 112 switchesbidirectional switches 2RU, 2TU, 2RV, 2TV, 2RW, 2TW on and off whilekeeping any of the bidirectional switches 2SU, 2SV, 2SW on. In the thirdsection, the power conversion control unit 112 switches bidirectionalswitches 2RU, 2SU, 2RV, 2SV, 2RW, 2SW on and off while keeping any ofthe bidirectional switches 2TU, 2TV, 2TW on. In the fourth section, thepower conversion control unit 112 switches the bidirectional switches2SU, 2TU, 2SV, 2TV, 2SW, 2TW on and off while keeping any of thebidirectional switches 2RU, 2RV, 2RW on. In the fifth section, the powerconversion control unit 112 switches the bidirectional switches 2RU,2TU, 2RV, 2TV, 2RW, 2TW on and off while keeping any of thebidirectional switches 2SU, 2SV, 2SW on. In the sixth section, the powerconversion control unit 112 switches the bidirectional switches 2RU,2SU, 2RV, 2SV, 2RW, 2SW on and off while keeping any of thebidirectional switches 2TU, 2TV, 2TW on. The length (phase angle) ofeach of the first section to the sixth section is ⅙ of a period (60°).Hereinafter, a period in which any one of the R phase, the S phase, andthe T phase is the positive reference phase (the first section, thethird section, and the fifth section) is referred to as a positivereference period, and a period in which any one of the R phase, the Sphase, and the T phase is the negative reference phase (the secondsection, the fourth section, and the sixth section) is referred to as anegative reference period.

The power conversion control unit 112 usually controls the phase of theprimary side current so that the primary side power factor is one inorder to maximize the utilization of the primary side voltage to thesecondary side voltage. The power conversion control unit 112 may adjustthe power factor on the primary side by shifting the first section tothe sixth section within a range in which the voltage of the R phasebecomes a positive peak value in the first section, the voltage of the Tphase becomes a negative peak value in the second section, the voltageof the S phase becomes the positive peak value in the third section, thevoltage of the R phase becomes the negative peak value in the fourthsection, and the voltage of the S phase becomes the negative peak valuein the sixth section. For example, the power conversion control unit 112shifts the center phases of the first section, the third section, andthe fifth section within a range of more than −30° and less than 30°with respect to the phase in which the voltages of the R phase, the Sphase, and the T phase become the positive peak value. In addition, thepower conversion control unit 112 shifts the center phases of the secondsection, the fourth section, and the sixth section within a range inwhich the voltages of the R phase, the S phase, and the T phase aregreater than −30° and less than 30° with respect to the negative peakvalue. Hereinafter, the center phases of the first section, the thirdsection, and the fifth section are referred to as a positive referencephase. The center phases of the second section, the fourth section, andthe sixth section are referred to as a negative reference phase. A phasein which the voltages of the R phase, the S phase, and the T phasebecome the positive peak value is referred to as “a primary sidepositive peak phase”. A phase in which the voltages of the R phase, theS phase, and the T phase become the negative peak value is referred toas “a primary side negative peak phase”.

The voltage command includes an amplitude command value and a phasecommand value. The amplitude command value is a command value for theoscillation amplitude of the secondary side voltage. A phase commandvalue is a command value for the phase of the secondary side voltage. Asan example, the amplitude command value corresponds to the magnitude ofa voltage command vector in a fixed coordinate system, and the phasecommand value corresponds to the rotation angle of the voltage commandvector in the fixed coordinate system. The fixed coordinate system is acoordinate system fixed to a stator of the electric device 92. Examplesof the fixed coordinate system include an αβ coordinate system having anα axis and a β axis orthogonal to each other as coordinate axes.

The power conversion control unit 112 obtains the amplitude commandvalue and the phase command value, and controls the matrix convertercircuitry 10 to output the secondary side voltage having oscillationamplitude and phase corresponding to the amplitude command value and thephase command value. The current information acquisition unit 113acquires information of the secondary side current. For example, thecurrent information acquisition unit 113 obtains a current value of thepower lines 12U, 12V, 12W from the current sensor 50.

The first mode control unit 114 is configured to cause the secondaryside frequency of the matrix converter circuitry 10 to follow thecommand frequency. The secondary side frequency means a frequency of thesecondary side voltage or the secondary side current. For example, thefirst mode control unit 114 controls the matrix converter circuitry 10so that the frequency of the secondary side voltage follows the commandfrequency. The frequency of the secondary side current follows thefrequency of the secondary side voltage. Therefore, causing thefrequency of the secondary side voltage to follow the command frequencyis synonymous with causing the frequency of the secondary side currentto follow the command frequency. Hereinafter, the control by the firstmode control unit 114 is referred to as “a first mode control”.

The second mode control unit 115 is configured to control the matrixconverter circuitry 10 according to the second control mode. Forexample, the second mode control unit 115 is configure to maintain theprimary-secondary phase difference within the predetermined targetrange. The primary side may comprise the primary side phase and aprimary side adjacent phase. An example of combination of the primaryside phase and the secondary side phase is a voltage phase of the Rphase and a voltage phase of the S phase. Another example of combinationof the primary side phase and the secondary side phase is the voltagephase of the S phase and a voltage phase of the T phase. Another exampleof combination of the primary side phase and the secondary side phase isthe voltage phase of the T phase and the voltage phase of the R phase.The second mode control unit 115 may further be configured to maintainthe primary-secondary phase difference within the target range andmaintain the secondary side phase between the primary side phase and theprimary side adjacent phase. In the three phase AC power, anintra-primary phase difference between the primary side phase and theprimary side adjacent phase is 120°. For example, the intra-primaryphase difference between the R phase and the S phase is 120°, theintra-primary phase difference between the S phase and the T phase isalso 120°, and the intra-primary phase difference between the T phaseand the R phase is also 120°. In that case, the second mode control unit115 may further be configured to maintain the primary-secondary phasedifference within the target range which is ±30° of an odd multiple of60°. The odd multiple of 60° may be a positive value or a negativevalue. Maintaining the primary-secondary phase difference within thetarget range means maintaining an absolute value of theprimary-secondary phase difference within the target range. For example,the second mode control unit 115 may maintain the difference between thesecondary side phase and the primary side phase at 45° to 75°, maymaintain the difference between the secondary side phase and the primaryside phase at 55° to 65°, and may maintain the difference between thesecondary side phase and the primary side phase at substantially 60°.

The secondary side phase is a phase of the secondary side voltage or thesecondary side current. The primary side phase is a phase of the primaryside voltage or the primary side current. The primary side phase may bea phase of the primary side voltage of the matrix converter circuitry 10(a primary side voltage phase of the matrix converter circuitry 10), andthe secondary side phase may be a phase of the primary side current ofthe matrix converter circuitry 10 (a secondary side current phase of thematrix converter circuitry 10). For example, the second mode controlunit 115 may further be configured to control the matrix convertercircuitry 10 so as to maintain the primary-secondary phase differencebetween the secondary side current phase acquired by the currentinformation acquisition unit 113 and the primary side voltage phasecalculated by the phase/amplitude calculation unit 111 within ±30° of anodd multiple of 60°. For example, the second mode control unit 115 mayfurther be configured to: calculate a deviation between a targetdifference predetermined within the target range and theprimary-secondary phase difference; calculate a voltage command toreduce the deviation; and cause the secondary side voltage of the matrixconverter circuitry 10 to follow the voltage command. Hereinafter, thecontrol by the second mode control unit 115 is referred to as “a secondmode control”.

The mode switching unit 116 is configured to: select the first controlmode in response to determining that the command-primary frequencydifference is above the predetermined threshold; and select the secondcontrol mode in response to determining that the command-primaryfrequency difference is below the threshold. The first mode control unit114 or the second mode control unit 115 controls the matrix convertercircuitry 10 in accordance with a selection of the first control mode orthe second control mode. For example, the first mode control unit 114controls the matrix converter circuitry if the mode switching unit 116selects the first control mode. The second mode control unit 115controls the matrix converter circuitry if the mode switching unit 116selects the second control mode. For example, the mode switching unit116 is configured to switch a control mode of the matrix convertercircuitry 10 based on the command-primary difference between the commandfrequency and the primary side frequency so that control by the firstmode control unit 114 is executed when the command-primary differenceexceeds the predetermined threshold and control by the second modecontrol unit 115 is executed when the command-primary difference isbelow the threshold. For example, the mode switching unit 116 shifts thecontrol by the first mode control unit 114 to the control by the secondmode control unit 115 when the difference between the command frequencyand the primary side frequency becomes equal to or less than apredetermined first threshold. The mode switching unit 116 may shiftcontrol by the second mode control unit 115 to control by the first modecontrol unit 114 in response to the difference between the commandfrequency and the primary side frequency exceeding a predeterminedsecond threshold. The primary side frequency means the frequency of theprimary side voltage or the primary side current.

For example, the mode switching unit 116 shifts control by the firstmode control unit 114 to control by the second mode control unit 115when the difference between the command frequency and the frequency ofthe primary side voltage falls below the first threshold, and shiftscontrol by the second mode control unit 115 to control by the first modecontrol unit 114 when the difference between the command frequency andthe frequency of the primary side voltage exceeds the second threshold.The first threshold and the second threshold may be equal or differentfrom each other. For example, the second threshold may be greater thanthe first threshold.

The frequency of the primary side voltage is substantially equal to thefrequency of the primary side current. Therefore, the difference betweenthe command frequency and the frequency of the primary side voltagefalling below the first threshold is synonymous with the differencebetween the command frequency and the frequency of the primary sidecurrent falling below the first threshold. That the difference betweenthe command frequency and the frequency of the primary side voltageexceeds the second threshold is synonymous with that the differencebetween the command frequency and the frequency of the primary sidecurrent exceeds the second threshold.

After the mode switching unit 116 shifts the control by the first modecontrol unit 114 to the control by the second mode control unit 115, thesecond mode control unit 115 may gradually change the difference betweenthe secondary side phase and the primary side phase from outside therange of the ±30° of an odd multiple of 60° to within the range beforemaintaining the difference between the secondary side phase and theprimary side phase within the ±30° of an odd multiple of 60°.

FIG. 3 is a graph illustrating transitions of the primary side voltageand the secondary side current before and after the mode switching unit116 shifts control by the first mode control unit 114 to control by thesecond mode control unit 115. In this graph, the horizontal axisrepresents an elapsed time, the vertical axis represents the magnitudeof the primary side voltage or the secondary side current, the solidline plot represents the transition of the primary side voltage, and thedashed line plot represents the transition of the secondary sidecurrent.

From a time t0 corresponding to the origin of the graph to a time t1,control is performed by the first mode control unit 114. In thiscontrol, the command frequency gradually increases, and in the time t1,the difference between the command frequency and the frequency of theprimary side voltage falls below the threshold first. The mode switchingunit 116 now shifts control by the first mode control unit 114 tocontrol by the second mode control unit 115.

The second mode control unit 115 gradually changes the differencebetween the phase of the secondary side current and the phase of theprimary side voltage up to 60° from the time t1 to a time t2. The secondmode control unit 115 then maintains the difference between the phase ofthe secondary side current and the phase of the primary side voltage atsubstantially 60°. By keeping the difference between the phase of thesecondary side current and the phase of the primary side voltage at 60°,the secondary side frequency becomes equal to the primary sidefrequency, but a state in which the phase of the secondary side currentand the phase of the primary side voltage are aligned is avoided.

The deterioration detection unit 117 is configured to: calculate adeterioration level based on the secondary side current, the carrierfrequency, and the primary-secondary frequency difference between aprimary side frequency and a secondary side frequency of the matrixconverter circuitry; and output a deterioration notification in responseto determining that the deterioration level exceeds a predeterminedlevel. For example, the deterioration detection unit 117 evaluates thedeterioration level of the switching element based on the information ofthe primary side voltage calculated by the phase/amplitude calculationunit 111, the command frequency, the information of the secondary sidecurrent acquired by the current information acquisition unit 113, andthe carrier frequency in the power conversion control unit 112.Hereinafter, configurations of the first mode control unit 114, thesecond mode control unit 115, and the deterioration detection unit 117will be described in more detail.

First Mode Control Unit

When the first mode control is selected by the mode switching unit 116,the first mode control unit 114 acquires the command frequency from thehost controller 200 and controls the matrix converter circuitry 10 sothat the secondary side frequency follows the command frequency. As anexample, as illustrated in FIG. 4, the first mode control unit 114includes a voltage command generation unit 121, an amplitude commandvalue calculation unit 122, and a phase command value calculation unit123, and repeats a series of control cycles by these units.

The voltage command generation unit 121 calculates a voltage command forthe secondary side voltage based on the command frequency w*. Forexample, the voltage command generation unit 121 calculates the voltagecommand vector in the rotating coordinate system by the V/f method. Therotating coordinate system is a coordinate system that rotates insynchronization with the command frequency. Examples of the rotatingcoordinate system include a γδ coordinate system in which a γ-axishaving a magnetic pole direction of the rotor as a target direction anda δ-axis perpendicular to the γ-axis are coordinate axes. The voltagecommand generation unit 121 may calculate the voltage command vectorbased on the detected value of the secondary side current, the torquecommand, and the like.

The amplitude command value calculation unit 122 calculates a commandvalue for oscillation amplitude of the secondary side voltage.Hereinafter, the command value for the oscillation amplitude of thesecondary side voltage is referred to as “the amplitude command value”.For example, the amplitude command value calculation unit 122 calculatesthe magnitude of the voltage command vector as the amplitude commandvalue |V|.

The phase command value calculation unit 123 calculates a command valuefor the phase of the secondary side voltage. Hereinafter, the commandvalue for the phase of the secondary side voltage is referred to as “thephase command value”. For example, the phase command value calculationunit 123 calculates a phase command value θ_(PWM) based on the angle ofrotation of the rotating coordinate system with respect to the fixedcoordinate system and the angle of phase of the voltage command vectorin the rotating coordinate system.

The amplitude command value calculation unit 122 outputs the amplitudecommand value |V| to the power conversion control unit 112, and thephase command value calculation unit 123 outputs the phase command valueθ_(PWM) to the power conversion control unit 112. The power conversioncontrol unit 112 controls the matrix converter circuitry 10 to outputthe secondary side voltage having an oscillation amplitude correspondingto the amplitude command value |V| and a phase corresponding to thephase command value θ_(PWM).

Second Mode Control Unit

The second mode control unit 115 may further be configured to: generatea target phase of the secondary side voltage phase to maintain theprimary-secondary phase difference within the target range; andcalculate the deviation based on a comparison between the target phaseand the secondary side voltage phase. The second mode control unit 115may further be configured to: detect a current-voltage phase differencebetween the secondary side voltage phase and the secondary side currentphase; and generate the target phase based on the current-voltage phasedifference. The second mode control unit 115 may further be configuredto: generate a target phase so that a target-primary phase differencebetween the target phase and the primary side voltage phase is withinthe target range; and calculate the deviation based on a comparisonbetween the target phase and the secondary side current phase. Forexample, when the second control mode is selected by the mode switchingunit 116, the second mode control unit 115 may generate a target phaseof the secondary side voltage phase to maintain the primary-secondaryphase difference within ±30° of an odd multiple of 60°, and control thematrix converter circuitry 10 so as to reduce the deviation between thetarget phase and the phase of the secondary side voltage. For example,the second mode control unit 115 may further be configured to cause anamplitude of the secondary side voltage (a secondary side voltageamplitude of the matrix converter circuitry 10) to follow an amplitudecommand value different from an amplitude of the primary side voltage (aprimary side voltage amplitude of the matrix converter circuitry 10).The second mode control unit 115 may generate the phase command valuebased on the deviation and controls the matrix converter circuitry 10 tooutput the secondary side voltage having the oscillation amplitudecorresponding to the amplitude command value and the phase correspondingto the phase command value. The second mode control unit 115 may set theamplitude command value to a value different from the oscillationamplitude of the primary side voltage.

As an example, as illustrated in FIG. 5, the second mode control unit115 includes a voltage command generation unit 136, an amplitude commandvalue calculation unit 131, a current-voltage phase difference detectionunit 133, a target phase calculation unit 132, and a phase command valuecalculation unit 134, and repeats a series of control cycles by theseunits.

Like the voltage command generation unit 121, the voltage commandgeneration unit 136 calculates the voltage command for the secondaryside voltage based on the command frequency ω*. For example, the voltagecommand generation unit 136 calculates the voltage command vector in therotating coordinate system by the V/f method. The voltage commandgeneration unit 136 may calculate the voltage command vector based onthe detected value of the secondary side current, the torque command,and the like.

The amplitude command value calculation unit 131 calculates theamplitude command value similarly to the amplitude command valuecalculation unit 122. For example, the amplitude command valuecalculation unit 131 calculates the magnitude of the voltage commandvector as the amplitude command value Vk. The amplitude command value|V| may be different from the oscillation amplitude of the primary sidevoltage. The current-voltage phase difference detection unit 133calculates the phase difference of the secondary side voltage withrespect to the phase of the secondary side current. Hereinafter, thedifference calculated by the current-voltage phase difference detectionunit 133 is referred to as “a current-voltage phase difference”.

For example, the current-voltage phase difference detection unit 133acquires the phase command value output to the power conversion controlunit 112 in the previous control cycle as information indicating thephase of the secondary side voltage. Hereinafter, the phase commandvalue is referred to as “the phase command value of the previous cycle”.Further, the current-voltage phase difference detection unit 133calculates the phase of the secondary side current based on a currentvalue Iu, Iv, Iw of the power lines 12U, 12V, 12W acquired by thecurrent information acquisition unit 113. Then, the current-voltagephase difference detection unit 133 calculates a current-voltage phasedifference based on the phase command value of the previous cycle andthe calculated phase of the secondary side current.

The target phase calculation unit 132 generates the target phase of thesecondary side voltage so that the difference between the phase of thesecondary side current and the phase of the primary side voltage has avalue of ±30° of an odd multiple of 60°. For example, the target phasecalculation unit 132 calculates a current target phase whose differencefrom the phase of the primary side voltage is ±30° of an odd multiple of60°. If the phase of the secondary side current leads the phase of theprimary side voltage, the target phase calculation unit 132 maycalculate the current target phase by adding ±30° of an odd multiple of60° to the phase of the primary side voltage. If the phase of thesecondary side current is behind the phase of the primary side voltage,the target phase calculation unit 132 may calculate the current targetphase by subtracting ±30° of an odd multiple of 60° from the phase ofthe primary side voltage. The target phase calculation unit 132generates the target phase of the secondary side voltage based on thecurrent-voltage phase difference calculated by the current-voltage phasedifference detection unit 133, and the current target phase. Forexample, the current-voltage phase difference may be calculated bysubtracting the secondary side current phase from the secondary sidevoltage phase. In that case, the target phase calculation unit 132 maygenerate the target phase of the secondary side voltage by adding thecurrent-voltage phase difference to the current target phase.

The phase command value calculation unit 134 calculates the phasecommand value based on a deviation between the target phase and thephase of the secondary side voltage. For example, the phase commandvalue calculation unit 134 calculates a deviation between the targetphase and the phase command value of the previous cycle, and calculatesthe phase command value so as to reduce the deviation. For example, thephase command value calculation unit 134 calculates the deviationbetween the target phase and the phase command value of the previouscycle, as illustrated in an addition point 141. The phase command valuecalculation unit 134 performs a proportional-integral operation on thedeviation, as indicated by a block 142. Further, the phase command valuecalculation unit 134 multiplies the result of the proportional-integraloperation by a period Ts of one control cycle to calculate a phasechange amount, as indicated by a block 143. Further, the phase commandvalue calculation unit 134 calculates a phase command value θ_(PWM2) byadding the phase change amount to the phase command value of theprevious cycle, as illustrated in an addition point 144.

The amplitude command value calculation unit 131 outputs the amplitudecommand value |V| to the power conversion control unit 112, and thephase command value calculation unit 134 outputs the phase command valueθ_(PWM2) to the power conversion control unit 112. The power conversioncontrol unit 112 controls the matrix converter circuitry 10 to outputthe secondary side voltage having an oscillation amplitude correspondingto the amplitude command value |V| and a phase corresponding to thephase command value θ_(PWM2).

As described above, since the current-voltage phase difference detectionunit 133 adds the phase change amount to the phase command value of theprevious cycle, a delay of one cycle is included in the phase commandvalue θ_(PWM2), and reduction of the deviation is delayed accordingly.Therefore, the second mode control unit 115 may further be configuredto: calculate a delay compensation value based on the primary sidefrequency; modify the phase command value based on the delaycompensation value, so as to compensate for a delay of the deviationreduction; and cause the secondary side voltage phase to follow themodified phase command value. The second mode control unit 115 mayfurther be configured to repeat a control cycle comprising: calculatingthe deviation; calculating the phase command value based on a previousphase command value calculated in a previous control cycle and thedeviation; calculating the delay compensation value based on the primaryside frequency; modifying the phase command value based on the delaycompensation value; and causing the secondary side voltage phase tofollow the modified phase command value. The second mode control unit115 may further be configured to calculate the delay compensation valuebased on the deviation and a cycle time of the control cycle. Forexample, the second mode control unit 115 may calculate the delaycompensation value based on the primary side frequency and add the delaycompensation value to the phase command value to compensate for thedelay of the deviation reduction. The second mode control unit 115 mayfurther be configured to: calculate the delay compensation valueaccording to a weighted average of the command frequency and the primaryside frequency; and gradually increase a weight of the primary sidefrequency in the delay compensation value after a shift from the firstcontrol mode to the second control mode. The second mode control unit115 may further be configured to gradually increase a weight of thecommand frequency in the delay compensation value before a shift fromthe second control mode to the first control mode. For example, thesecond mode control unit 115 further comprises a compensation valuecalculation unit 135.

The compensation value calculation unit 135 calculates the delaycompensation value based on the primary side frequency win. For example,the compensation value calculation unit 135 calculates the delaycompensation value by multiplying the primary side frequency win by theperiod Ts. As illustrated in an addition point 147, the phase commandvalue calculation unit 134 adds the delay compensation value to thephase command value of the previous cycle to calculate a phaseestimation value of the current secondary side voltage, and inputs thephase estimation value to the addition point 144. Accordingly, the phasecommand value θ_(PWM2) is calculated by adding the phase change amountto the current phase estimation value of the secondary side voltage.

As the command frequency ω* approaches the primary side frequency win asthe first mode control shifts to the second mode control, thecompensation value calculation unit 135 may calculate the delaycompensation value based on a weighted average of the command frequencyω* and the primary side frequency ωin. For example, the compensationvalue calculation unit 135 calculates the delay compensation value bymultiplying the weighted average by the period Ts. After the modeswitching unit 116 shifts the first mode control to the second modecontrol, the compensation value calculation unit 135 gradually increasesthe weight of the primary side frequency win in the delay compensationvalue and gradually decreases the weight of the command frequency ω*. Asa result, the secondary side frequency is shifted from the commandfrequency ω* to the primary side frequency win, the shift from the firstmode control to the second mode control becomes smoother, and control inthe second mode becomes more stable.

Further, the compensation value calculation unit 135 may graduallyincrease the weight of the command frequency ω* and gradually decreasethe weight of the primary side frequency ωin in the delay compensationvalue before the mode switching unit 116 shifts the second mode controlto the first mode control. For example, the mode switching unit 116outputs a shift preparation command to the second mode control unit 115when the difference between the command frequency and the frequency ofthe primary side voltage exceeds the second threshold. Correspondingly,the compensation value calculation unit 135 gradually increases theweight of the command frequency ω* in the delay compensation value andgradually decreases the weight of the primary side frequency ωin. Duringthis period, the second mode control is continued. The second modecontrol unit 115 outputs a preparation completion notification to themode switching unit 116 when the weight of the primary side frequencywin in the delay compensation value becomes zero. Accordingly, the modeswitching unit 116 shifts the second mode control to the first modecontrol.

The second mode control unit 115 may generate the target phase for thesecondary side current instead of the target phase for the secondaryside voltage, and control the matrix converter circuitry 10 to reducethe deviation between the target phase and the phase of the secondaryside current. For example, the second mode control unit 115 maycalculate the phase command value θ_(PWM2) by calculating a phase changeamount by performing a proportional-integral operation or the like on adeviation between the target phase and the phase of the secondary sidecurrent, and adding the phase change amount to the phase estimationvalue of the secondary side voltage.

Deterioration Detection Unit

The deterioration detection unit 117 may be configured to: estimate anaverage heating value (an average heating level) based on the secondaryside current and the carrier frequency; calculate a concentrationcoefficient based on a primary-secondary frequency difference betweenthe primary side frequency and the secondary side frequency; estimate alocal heating level based on the average heating value and theconcentration coefficient; calculate the deterioration level based onthe local heating level; and notify that the deterioration level exceedsa predetermined level.

For example, as illustrated in FIG. 6, the deterioration detection unit117 includes an average temperature rise estimation unit 151, acoefficient calculation unit 152, a local temperature rise estimationunit 153, a deterioration level calculation unit 154, a comparison unit157, and a notification unit 158. The average temperature riseestimation unit 151 is configured to estimate the average heating valuebased on the secondary side current and the carrier frequency. Forexample, the average temperature rise estimation unit 151 calculates theaverage heating value based on the following expression.

T=A·I2+(B+C·fc+D)·I   (1)

-   ΔT: average heating value-   I: oscillation amplitude of the secondary side current-   fc: carrier frequency-   A, B, C, D: coefficients

The coefficients A, B, C, and D are obtained in advance by an actualmachine test or simulation. The average heating value calculated byExpression (1) includes a steady loss caused by conduction of thesecondary side current and the switching loss caused by on/off of theswitching element.

The coefficient calculation unit 152 is configured to calculate theconcentration coefficient based on the primary-secondary frequencydifference. For example, the coefficient calculation unit 152 acquiresinformation on the difference between the primary side frequency and thecommand frequency from the mode switching unit 116, and calculates theconcentration coefficient based on the information. In detail, thecoefficient calculation unit 152 increases the concentration coefficientas the absolute difference between the primary side frequency and thecommand frequency decreases. For example, the deterioration detectionunit 117 further comprises a coefficient profile storage unit 161.

The coefficient profile storage unit 161 (a profile storage device)stores a coefficient profile representing the relationship between theabsolute value of the primary-secondary phase difference and theconcentration coefficient such that the concentration coefficientincreases as the absolute value of the primary-secondary frequencydifference decreases. The primary-secondary frequency difference may bea difference between the primary side frequency and the commandfrequency (the command-primary frequency difference). The coefficientprofile stored in the coefficient profile storage unit 161 may be adiscrete data sequence or a function.

The coefficient calculation unit 152 may further be configured tocalculate the concentration coefficient based on the absolute value ofthe primary-secondary frequency difference and the coefficient profile.For example, the coefficient calculation unit 152 derives theconcentration coefficient corresponding to the absolute differencebetween the primary side frequency and the command frequency in thecoefficient profile.

FIG. 7 is a graph illustrating the coefficient profile, in which thehorizontal axis represents the magnitude of the absolute value of thedifference and the vertical axis represents the concentrationcoefficient. The coefficient profile is determined such that theconcentration coefficient is zero when the absolute difference value isequal to or greater than the predetermined threshold f1, and theconcentration coefficient gradually increases as the absolute differencevalue decreases when the absolute difference value is less than thethreshold f1.

The local temperature rise estimation unit 153 is configured to estimatethe local heating level based on the average heating value (the averageheating level) and the concentration coefficient. For example, the localtemperature rise estimation unit 153 calculates the local heating levelby multiplying the average heating value by the concentrationcoefficient. In the case where the coefficient profile is determined asillustrated in FIG. 7, when the absolute values of the differences areequal to or larger than the threshold f1, the local heating level is setto zero, and the progress of deterioration due to temperature rise isignored.

The deterioration level calculation unit 154 is configured to calculatethe deterioration level of the switching element based on the localheating level. For example, the deterioration level calculation unit 154may further be configured to: calculate a deterioration progress basedon the local heating level; and integrate the deterioration progress toupdate the deterioration level. The deterioration level calculation unit154 may calculate the deterioration level by repeatedly calculating thedeterioration progress based on the local heating level and integratingthe deterioration progress in the control cycle.

One of the causes of the deterioration of the switching element due tothe temperature rise is shrinkage of a conductive portion caused by thetemperature rise and the temperature fall, and therefore thedeterioration level of the switching element is also affected by thefrequency of repetition of the temperature rise and the temperaturefall. Therefore, the deterioration level calculation unit 154 mayfurther be configured to: calculate a temperature rise frequency basedon the primary-secondary frequency difference; and integrate thedeterioration progress at the temperature rise frequency to update thedeterioration level. For example, the deterioration level calculationunit 154 may be further configured to calculate the deterioration levelby repeatedly calculating the deterioration progress based on the localheating level, calculating the temperature rise frequency based on theprimary-secondary frequency difference, and integrating a result ofmultiplying the deterioration progress by the temperature risefrequency. For example, the deterioration level calculation unit 154includes a deterioration profile storage unit 162, a deteriorationprogress calculation unit 155, a frequency calculation unit 156, and anintegration unit 159, and the deterioration progress is repeatedlyintegrated by these units.

The deterioration profile storage unit 162 (deterioration profilestorage device) stores a deterioration profile representing arelationship between the local heating level and the deteriorationprogress. FIG. 8 is a graph illustrating a deterioration profile,wherein the horizontal axis represents the local heating level and thevertical axis represents the deterioration progress. The deteriorationprofile indicates that the deterioration progress increases as the localheating level increases. For example, the deterioration profile may bedefined such that the deterioration progress is zero when the localheating level is equal to or less than a predetermined threshold T1, andthe deterioration progress increases as the local heating levelincreases when the local heating level exceeds the threshold T1.Furthermore, the deterioration profile may be defined such that thedeterioration progress is constant when the local heating level is equalto or greater than a threshold T2, which is greater than the thresholdT1.

The deterioration progress may be a value obtained by converting thedeterioration of the switching element into the number of times ofrepetition of temperature increase and temperature decrease. Since thelifetime (an allowable deterioration level) of the switching element maybe determined by the number of times of repetition of temperatureincrease/decrease, when the deterioration progress is represented by thenumber of times of repetition of temperature increase/decrease, acomparison between the deterioration level and the lifetime can befacilitated.

The deterioration progress calculation unit 155 is configured tocalculate the deterioration progress based on the local heating leveland the deterioration profile. For example, the deterioration progresscalculation unit 155 derives the deterioration progress corresponding tothe local heating level in the deterioration profile.

The frequency calculation unit 156 calculates the frequency of localtemperature rise occurring per unit time (for example, per one second).The temperature of the switching element locally increases during aperiod in which the phase of the primary side voltage and the phase ofthe secondary side current are aligned, and gradually decreases as thephase difference between the phase of the primary side voltage and thephase of the secondary side current increases. Therefore, it can be saidthat the frequency at which the phase of the primary side voltage andthe phase of the secondary side current are aligned per unit time issubstantially proportional to the frequency of the local temperaturerise. Therefore, the frequency calculation unit 156 calculates thedifference between the primary side frequency and the secondary sidefrequency as the frequency of local temperature rise. For example, thefrequency calculation unit 156 calculates the absolute differencebetween the primary side frequency and the command frequency as thefrequency of local temperature rise.

The integration unit 159 integrates the deterioration progresscalculated by the deterioration progress calculation unit 155 at thefrequency calculated by the frequency calculation unit 156. For example,the integration unit 159 multiplies the deterioration progress by thefrequency to calculate the deterioration progress per unit time, andfurther multiplies the deterioration progress by the period Ts of thecontrol cycle to calculate the deterioration progress per one cycle.Then, the deterioration progress per one cycle is added to thedeterioration level calculated in the previous control cycle.

The comparison unit 157 compares the deterioration level calculated bythe deterioration level calculation unit 154 with the predeterminedlevel. The notification unit 158 notifies that the deterioration levelexceeds the predetermined level. For example, the notification unit 158displays on a display such as a liquid crystal monitor that thedeterioration level has exceeded the predetermined level. Thenotification unit 158 may output a notification signal to the hostcontroller 200 that the deterioration level has exceeded thepredetermined level.

As described above, as the difference between the primary side frequencyand the secondary side frequency decreases, the time during which thestate in which the phase of the primary side voltage is aligned with thephase of the secondary side current continues increases. Therefore, asthe difference between the primary side frequency and the secondary sidefrequency becomes smaller, the local temperature rise value of any ofthe switching elements of the matrix converter circuitry 10 becomeslarger, and the fluctuation width of the temperature due to this alsobecomes larger. The deterioration detection unit 117 may therefore beconfigured to evaluate the deterioration level of the switching elementin consideration of the temperature fluctuation and to notify thedeterioration of the switching element at an appropriate timing.

In the first control mode, the difference between the secondary sidephase and the primary side phase of the matrix converter circuitry 10can be changed without limitation. On the other hand, in the secondcontrol mode, the difference between the secondary side phase and theprimary side phase is maintained with in the target range. When the modeswitching unit 116 shifts the first mode control to the second modecontrol, a state in which the phase of the primary side voltage and thephase of the secondary side current are aligned is forcibly avoided, andthus the occurrence of local temperature rise is suppressed.Correspondingly, the coefficient calculation unit 152 may further beconfigured to decrease the concentration coefficient in response to ashift from the first control mode to the second control mode. Forexample, the coefficient calculation unit 152 may set the concentrationcoefficient to zero as the first mode control shifts to the second modecontrol.

The mode switching unit 116 corresponds to a state transition unitconfigured to shift a state in the matrix converter circuitry from afirst state to a second state having a smaller switching loss than thefirst state in response to the primary-secondary frequency differencefalling below a predetermined threshold. Shifting the first control modeto the second control mode is an example of shifting the switching statein the matrix converter circuitry 10 from the first state to the secondstate having a smaller switching loss than the first state in responseto the primary-secondary frequency difference falling below apredetermined threshold. The second state may be a state in which thetotal loss (power loss) of the switching loss and the steady loss issmaller than that in the first state.

A switching of a connection between the primary side and the secondaryside of the matrix converter circuitry 10 in the second state isperformed less frequently than in the first state. For example, thefirst state may be a state in which a switching of a connection betweenthe primary side and the secondary side of the matrix convertercircuitry 10 is performed, and the second state may be a state in whichthe switching of the connection is performed less frequently than in thefirst state. For example, the second state may be a state in which thecarrier frequency is lower than that in the first state. For example,the switching of the connection state is repeatedly performed with afirst carrier frequency in the first state, the switching of theconnection is repeatedly performed with a second carrier frequency thatis smaller than the first carrier frequency, in the second state.

A primary line of the primary side and a secondary line of the secondaryside may be repeatedly connected and disconnected in the first state,and an electrical connection between the primary line and the secondaryline may be maintained in the second state. For example, the secondstate may be a state in which the primary side and the second side aredirectly connected by the matrix converter circuitry 10. For example,the second state may be a state in which the power lines 11R, 11S, 11T(primary line) and the power lines 12U, 12V, 12W (secondary line) aredirectly connected by the matrix converter circuitry 10.

Hardware Configuration of Control Circuitry

FIG. 9 is a block diagram illustrating a hardware configuration of thecontrol circuitry 100. As illustrated in FIG. 9, the control circuitry100 includes a processor 191, a memory 192, a storage 193, acommunication port 194, an input/output port 195, and a switch controlcircuitry 196. The processor 191 may include multiple processingdevices, the memory 192 may include multiple memory devices, and thestorage 193 may include multiple storage devices.

The storage 193 includes a computer-readable storage medium, such as anon-volatile semiconductor memory. The storage 193 stores a program tocause the control circuitry 100 to perform a power conversion methodcomprising: a first mode control that includes causing a secondary sidefrequency of a matrix converter circuitry 10 to follow a commandfrequency by the matrix converter circuitry 10 performing bidirectionalpower conversion between primary side power and secondary side power; asecond mode control that includes maintaining, by the matrix convertercircuitry 10, a difference between a secondary side phase and a primaryside phase of the matrix converter circuitry 10 within ±30° of an oddmultiple of 60°; and a mode switching that includes switching a controlmode of the matrix converter circuitry 10 based on a difference betweenthe command frequency and a primary side frequency of the matrixconverter circuitry 10 and a predetermined threshold so that control bythe first mode control unit 114 is performed if the difference is abovethe threshold, and control by the second mode control unit 115 isperformed if the difference is below the threshold. The storage 193 maystore a program to cause the control circuitry 100 to perform a powerconversion method including estimating the average heating value (theaverage heating level) based on the secondary side current of the matrixconverter circuitry 10 performing bidirectional power conversion betweenthe primary side power and the secondary side power, calculating theconcentration coefficient based on the difference between the primaryside frequency and the secondary side frequency of the matrix convertercircuitry 10, estimating the local heating level based on the averageheating value and the concentration coefficient, calculating thedeterioration level based on the local heating level, and notifying thatthe deterioration level has exceeded the predetermined level. Forexample, the storage 193 stores a program for configuring each of thefunctional blocks in the control circuitry 100.

The memory 192 temporarily stores a program loaded from a storage mediumof the storage 193 and an operation result by the processor 191. Theprocessor 191 constitutes each functional block of the control circuitry100 by executing the program in cooperation with the memory 192. Theinput/output port 195 inputs and outputs an electric signal between thevoltage detection circuit 40 and the current sensor 50 in accordancewith a command from the processor 191. The communication port 194performs information communication with the host controller 200 inaccordance with a command from the processor 191. The switch controlcircuitry 196 outputs a drive signal for switching on and off thebidirectional switches 2RU, 2SU, 2TU, 2RV, 2SV, 2TV, 2RW, 2SW, 2TW tothe matrix converter circuitry 10 in accordance with a command from theprocessor 191.

It should be noted that the control circuitry 100 is not necessarilylimited to one that configures each function by a program. For example,at least a part of the functions of the control circuitry 100 may beconfigured by a dedicated logic circuit or an application specificintegrated circuit (ASIC) in which the dedicated logic circuit isintegrated.

Power Conversion Procedure

Next, a control procedure of the matrix converter circuitry 10 executedby the control circuitry 100 will be described as an example of powerconversion methods. The control procedure comprises: a first modecontrol that includes causing a secondary side frequency of a matrixconverter circuitry 10 to follow a command frequency by the matrixconverter circuitry 10 performing bidirectional power conversion betweenprimary side power and secondary side power; a second mode control thatincludes maintaining, by the matrix converter circuitry 10, a differencebetween a secondary side phase and a primary side phase of the matrixconverter circuitry 10 within ±30° of an odd multiple of 60°; and a modeswitching that includes switching a control mode of the matrix convertercircuitry 10 based on a difference between the command frequency and aprimary side frequency of the matrix converter circuitry 10 and apredetermined threshold so that control by the first mode control unit114 is performed if the difference is above the threshold, and controlby the second mode control unit 115 is performed if the difference isbelow the threshold. The control procedure may further includeestimating the average heating level based on the secondary side currentof the matrix converter circuitry 10 performing bidirectional powerconversion between the primary side power and the secondary side power,calculating the concentration coefficient based on the differencebetween the primary side frequency and the secondary side frequency ofthe matrix converter circuitry 10, estimating the local heating value(the local heating level) based on the average heating value and theconcentration coefficient, calculating the deterioration level based onthe local heating level, and notifying that the deterioration levelexceeds the predetermined level.

For example, the control circuitry 100 executes a control mode switchingprocedure, a first mode control procedure, a second mode controlprocedure, and a deterioration detection procedure in parallel.Hereinafter, each procedure will be described in detail.

Control Mode Switching Procedure

As illustrated in FIG. 10, the control circuitry 100 executes operationsS01, S02, S03, S04, S05, S06 in sequence. In the operation S01, the modeswitching unit 116 outputs a first mode command to the first modecontrol unit 114. In response, the first mode control unit 114 initiatesa first mode control procedure. In the operation S02, the mode switchingunit 116 waits for the difference between the command frequency and theprimary side frequency to fall below the first threshold. In theoperation S03, the mode switching unit 116 outputs a second mode commandto the second mode control unit 115. In response, the second modecontrol unit 115 initiates a second mode control procedure. In theoperation S04, the mode switching unit 116 waits for the differencebetween the command frequency and the primary side frequency to exceedthe second threshold.

In the operation 505, the mode switching unit 116 outputs a shiftpreparation command to the first mode control to the second mode controlunit 115. In response, the second mode control unit 115 initiates shiftpreparation to first mode control as described below. In the operationS06, the mode switching unit 116 waits for completion of the shiftpreparation by the second mode control unit 115. The control circuitry100 then returns processing to the operation S01. Thus, the first modecontrol procedure by the first mode control unit 114 is resumed again.The control circuitry 100 repeats the above procedure.

First Mode Control Procedure

As illustrated in FIG. 11, the control circuitry 100 executes aoperation S11 to S16 in sequence. In the operation S11, the first modecontrol unit 114 waits for the output of the first mode command from themode switching unit 116. In the operation S12, the voltage commandgeneration unit 121 calculates a voltage command vector for thesecondary side voltage based on the command frequency ω*. In theoperation S13, the amplitude command value calculation unit 122calculates the magnitude of the voltage command vector as the amplitudecommand value. In the operation S14, the phase command value calculationunit 123 calculates the phase command value based on the angle ofrotation of the rotating coordinate system with respect to the fixedcoordinate system and the angle of phase of the voltage command vectorin the rotating coordinate system. In the operation S15, the amplitudecommand value calculation unit 122 outputs the amplitude command valueto the power conversion control unit 112, and the phase command valuecalculation unit 123 outputs the phase command value to the powerconversion control unit 112. The power conversion control unit 112controls the matrix converter circuitry 10 to output the secondary sidevoltage having an oscillation amplitude corresponding to the oscillationamplitude of the secondary side voltage and a phase corresponding to thephase command value.

In the operation S16, the first mode control unit 114 checks whether ornot the second mode command is output from the mode switching unit 116.If it is determined that the second mode command is not output in theoperation S16, the control circuitry 100 returns the processing to theoperation S12. Thereafter, the first mode control procedure is repeateduntil the mode switching unit 116 outputs the second mode command. If itis determined that the second mode command is output in the operationS16, the control circuitry 100 completes the first mode controlprocedure.

Second Mode Control Procedure

As illustrated in FIG. 12, the control circuitry 100 first executesoperations S21, S22, S23, S24. In the operation S21, the second modecontrol unit 115 waits for the output of the second mode command fromthe mode switching unit 116. In the operation S22, the compensationvalue calculation unit 135 starts gradually increasing the weight of theprimary side frequency and gradually decreasing the weight of thecommand frequency in the delay compensation value. In the operation S23,the second mode control unit 115 executes phase tracking control tomaintain the difference between the phase of the secondary side currentand the phase of the primary side voltage within ±30° of an odd multipleof 60°. Contents of the operation S23 will be described later. In theoperation S24, the second mode control unit 115 confirms whether or notthe shift preparation command to the first mode control is output fromthe mode switching unit 116.

If it is determined that the shift preparation command is not output inthe operation S24, the control circuitry 100 returns the processing tothe operation S23. Thereafter, the phase tracking control is continueduntil the shift preparation command is output.

If it is determined that the shift preparation command is output in theoperation S24, the control circuitry 100 executes operations S25, S26,S27. In the operation S25, the compensation value calculation unit 135starts gradually increasing the weight of the command frequency in thedelay compensation value and gradually decreasing the weight of theprimary side frequency. In the operation S26, the second mode controlunit 115 executes the phase tracking control. In the operation S27, thesecond mode control unit 115 checks whether the weight of the primaryside frequency in the delay compensation value has reached zero.

If it is determined in the operation S27 that the weight of the primaryside frequency in the delay compensation value has not reached zero, thecontrol circuitry 100 returns processing to the operation S26.Thereafter, the phase tracking control is continued until the weight ofthe primary side frequency in the delay compensation value reaches zero.If it is determined in the operation S27 that the weight of the primaryside frequency in the delay compensation value reaches zero, the controlcircuitry 100 completes the second mode control procedure.

FIG. 13 is a flowchart illustrating a phase tracking control procedurein operations S23, S26. As illustrated in FIG. 13, the control circuitry100 executes operations S31, S32, S33, S34, S35, S36, S37, S38, S39 insequence. In the operation S31, the voltage command generation unit 136calculates a voltage command vector for the secondary side voltage basedon the command frequency ω*. In the operation S32, the amplitude commandvalue calculation unit 131 calculates the magnitude of the voltagecommand vector as the amplitude command value.

In the operation S33, the current information acquisition unit 113acquires information of the secondary side current. For example, thecurrent information acquisition unit 113 obtains a current value of thepower lines 12U, 12V, 12W from the current sensor 50. In the operationS34, the current-voltage phase difference detection unit 133 calculatesthe phase difference of the secondary side voltage with respect to thephase of the secondary side current (the current-voltage phasedifference).

In the operation S35, the target phase calculation unit 132 generatesthe target phase of the secondary side voltage such that the differencebetween the phase of the secondary side current and the phase of theprimary side voltage is ±30° of an odd multiple of 60°. For example, thetarget phase calculation unit 132 calculates a current target phasewhose difference from the phase of the primary side voltage is ±30° ofan odd multiple of 60°, and generates the target phase of the secondaryside voltage by adding a current-voltage phase difference to the currenttarget phase. In the operation S36, the phase command value calculationunit 134 calculates a deviation between the target phase and the phasecommand value of the previous cycle, and calculates the phase changeamount for reducing the deviation.

In the operation S37, the compensation value calculation unit 135calculates the delay compensation value. In the operation S38, the phasecommand value calculation unit 134 adds the delay compensation value tothe phase command value of the previous cycle to calculate a phaseestimation value of the current secondary side voltage, and adds thephase change amount to the phase estimation value to calculate the phasecommand value.

In the operation S39, the amplitude command value calculation unit 131outputs the amplitude command value to the power conversion control unit112, and the phase command value calculation unit 134 outputs the phasecommand value to the power conversion control unit 112. The powerconversion control unit 112 controls the matrix converter circuitry 10to output the secondary side voltage having an oscillation amplitudecorresponding to the amplitude command value and a phase correspondingto the phase command value. Thus, the phase follow-up control procedureof one cycle is completed. It should be noted that the execution orderof the operations can be variously changed.

Deterioration Detection Procedure

As illustrated in FIG. 14, the control circuitry 100 first executesoperations S41, S42, S43, S44, S45, S46, S47. In the operation S41, theaverage temperature rise estimation unit 151 estimates the averageheating value based on the secondary side current and the carrierfrequency. In the operation S42, the coefficient calculation unit 152calculates the concentration coefficient based on the difference betweenthe primary side frequency and the secondary side frequency. In theoperation S43, the local temperature rise estimation unit 153 estimatesthe local heating level based on the average heating value and theconcentration coefficient. In the operation S44, the deteriorationprogress calculation unit 155 calculates the deterioration progressbased on the local heating level and the deterioration profile.

In the operation S45, the frequency calculation unit 156 calculates thedifference between the primary side frequency and the secondary sidefrequency as the frequency of local temperature rise. In the operationS46, the integration unit 159 calculates the deterioration level byintegrating the deterioration progress calculated by the deteriorationprogress calculation unit 155 with the frequency calculated by thefrequency calculation unit 156. In the operation S47, the comparisonunit 157 checks whether the deterioration level calculated by thedeterioration level calculation unit 154 exceeds the predeterminedlevel.

If the operation S47 determines that the deterioration level does notexceed the predetermined level, the control circuitry 100 returnsprocessing to the operation S41. Thereafter, until the deteriorationlevel exceeds the predetermined level, the calculation of thedeterioration progress and the frequency and the integration of thedeterioration progress by the calculation result of the frequency arerepeated.

If the operation S47 determines that the deterioration level exceeds thepredetermined level, the control circuitry 100 executes a operation S48.In the operation S48, the notification unit 158 notifies that thedeterioration level exceeds the predetermined level. This completes thedeterioration detection procedure.

As described above, the power conversion apparatus 1 may comprise:matrix converter circuitry 10 configured to perform bidirectional powerconversion between primary side power and secondary side power; a firstmode control unit 114 configured to cause a secondary side frequency ofthe matrix converter circuitry 10 to follow a command frequency; asecond mode control unit 115 configured to maintain the differencebetween a secondary side phase and a primary side phase of the matrixconverter circuitry 10 within ±30° of an odd multiple of 60°; and a modeswitching unit 116 configured to switch a control mode of the matrixconverter circuitry 10 based on a difference between the commandfrequency and a primary side frequency of the matrix converter circuitry10 and a predetermined threshold so that control by the first modecontrol unit 114 is performed if the difference is above the threshold,and control by the second mode control unit 115 is performed if thedifference is below the threshold.

In the matrix converter circuitry, when the state in which the secondaryside phase and the primary side phase are aligned is maintained, lossdue to the switching is concentrated on any of the switching element ofthe matrix converter circuitry, and heat generation in the switchingelement becomes large.

In order to suppress the loss in the state where the secondary sidephase and the primary side phase are aligned, the secondary side and theprimary side may be directly connected by the matrix convertercircuitry, but in the state where the secondary side and the primaryside are directly connected, the secondary side oscillation amplitudecannot be controlled.

In contrast, according to the power conversion apparatus 1, the controlby the first mode control unit 114 is switched to the control by thesecond mode control unit 115 as the secondary side frequency approachesthe primary side frequency. The second mode control unit 115 maintainsthe difference between the secondary side phase and the primary sidephase within ±30° of an odd multiple of 60° by the matrix convertercircuitry 10. As a result, a state in which the secondary side phase andthe primary side phase are aligned is avoided, and thus heat generationof the switching element is suppressed. Further, the freedom of controlof the secondary side oscillation amplitude is maintained during thecontrol by the second mode control unit 115. Therefore, both the degreeof freedom in controlling the secondary side power and the suppressionof heat generation of the switching element may be achieved.

The second mode control unit 115 may be further configured to: generatea target phase of a secondary side voltage of the matrix convertercircuitry 10 such that a difference between a phase of a secondary sidecurrent of the matrix converter circuitry 10 and a phase of a primaryside voltage of the matrix converter circuitry 10 is ±30° of an oddmultiple of 60°; and control the matrix converter circuitry 10 to reducea deviation between the target phase and a phase of the secondary sidevoltage. Accordingly, heat generation in the switching element can bemore reliably suppressed. The loss in the switching element is maximizedwhen a phase at which the secondary side current becomes a positive peakvalue (hereinafter, referred to as “a second side positive peak value”)is the positive reference value (the center phases of the first section,the third section, and the fifth section) and minimized when the phasedifference between the second side positive peak value and the positivereference value is an odd multiple of 60°. Therefore, when the powerfactor on the primary side is one (when the positive reference phasecoincides with the primary side positive peak phase), the loss in theswitching element can be reduced by setting the difference between thephase of the secondary side current and the primary side voltage to ±30°of an odd multiple of 60°. As described above, the power conversioncontrol unit 112 may shift the positive reference phase from the primaryside positive peak phase for power factor adjustment of the primary sidepower. Accordingly, the phase shift range is often limited to a range ofmore than −30° and less than 30°. Therefore, even in such a case, if thedifference between the phase of the secondary side current and the phaseof the primary side voltage is ±30° of an odd multiple of 60°, the lossin the switching element is smaller than at least the case where thereis no phase difference between the secondary side current and theprimary side voltage.

The second mode control unit 115 may be further configured to: generatea target phase so that a difference between the target phase and a phaseof a primary side voltage of the matrix converter circuitry 10 is ±30°of an odd multiple of 60°; and control the matrix converter circuitry 10to reduce a deviation between the target phase and a phase of asecondary side current of the matrix converter circuitry 10.Accordingly, heat generation in the switching element can be morereliably suppressed.

The second mode control unit 115 may be further configured to generate aphase command value based on the deviation and control the matrixconverter circuitry 10 to output the secondary side voltage having aphase corresponding to the phase command value. Accordingly, the phaseof the secondary side voltage can quickly follow the target phase.

The second mode control unit 115 may be further configured to: calculatea delay compensation value based on the primary side frequency; and addthe delay compensation value to the phase command value, so as tocompensate for a reduction delay of the deviation. Accordingly, thephase of the secondary side voltage can follow the target phase morequickly.

The second mode control unit 115 may be further configured to: calculatethe delay compensation value according to a weighted average of thecommand frequency and the primary side frequency; and gradually increasea weight of the primary side frequency in the delay compensation valueafter the mode switching unit 116 shifts control by the first modecontrol unit 114 to control by the second mode control unit 115.Accordingly, the control by the first mode control unit 114 can besmoothly shifted to the control by the second mode control unit 115.

The second mode control unit 115 may be further configured to graduallyincrease a weight of the command frequency in the delay compensationvalue before the mode switching unit 116 shifts control by the secondmode control unit 115 to control by the first mode control unit 114.Accordingly, the control by the second mode control unit 115 can besmoothly shifted to the control by the first mode control unit 114.

The second mode control unit 115 may be further configured to controlthe matrix converter circuitry 10 to output the secondary side voltagehaving an oscillation amplitude corresponding to an amplitude commandvalue different from an oscillation amplitude of the primary sidevoltage. Accordingly, the degree of freedom of control may be utilized.

The power conversion apparatus 1 may further comprise: an averagetemperature rise estimation unit 151 configured to estimate an averageheating value (an average heating level) based on the secondary sidecurrent and a carrier frequency; a coefficient calculation unit 152configured to calculate a concentration coefficient based on adifference between the primary side frequency and the command frequency;a local temperature rise estimation unit 153 configured to estimate alocal heating level based on the average heating level and theconcentration coefficient; a deterioration level calculation unit 154configured to calculate a deterioration level based on the local heatinglevel; and a notification unit 158 configured to notify that thedeterioration level exceeds a predetermined level. Accordingly, thereliability of the matrix converter circuitry 10 can be further improvedby a combination of the evaluation of the deterioration level inconsideration of the concentration of loss that is likely to occur asthe secondary side frequency approaches the primary side frequency andthe suppression of the concentration of loss by switching the controlmode.

The deterioration level calculation unit 154 may be further configuredto calculate the deterioration level by repeatedly calculating adeterioration progress based on the local heating level and integratinga result of multiplying the deterioration progress. Accordingly, thedeterioration level may be evaluated.

The deterioration level calculation unit 154 may be further configuredto calculate the deterioration level by repeatedly calculating adeterioration progress based on the local heating level, calculating atemperature rise frequency based on a difference between the primaryside frequency and the command frequency, and integrating a result ofmultiplying the deterioration progress by the temperature risefrequency. Accordingly, the deterioration level may be evaluated.

The coefficient calculation unit 152 may be further configured todecrease the concentration coefficient in response to a shift fromcontrol by the first mode control unit 114 to control by the second modecontrol unit 115. Accordingly, overestimation of the deterioration levelcan be suppressed, and the matrix converter circuitry 10 can beefficiently used.

It is to be understood that not all aspects, advantages and featuresdescribed herein may necessarily be achieved by, or included in, any oneparticular example. Indeed, having described and illustrated variousexamples herein, it should be apparent that other examples may bemodified in arrangement and detail.

What is claimed is:
 1. A power conversion apparatus, comprising: matrixconverter circuitry configured to perform bidirectional power conversionbetween a primary side and a secondary side; and control circuitryconfigured to: select a first control mode in response to determiningthat a command-primary frequency difference between a command frequencyand a primary side frequency of the matrix converter circuitry is abovea predetermined threshold, wherein the first control mode includescausing a secondary side frequency of the matrix converter circuitry tofollow the command frequency; select a second control mode in responseto determining that the command-primary frequency difference is belowthe threshold, wherein the second control mode includes maintaining aprimary-secondary phase difference between a secondary side phase and aprimary side phase of the matrix converter circuitry within apredetermined target range; and control the matrix converter circuitryin accordance with a selection of the first control mode or the secondcontrol mode.
 2. The power conversion apparatus according to claim 1,wherein the primary side comprises the primary side phase and a primaryside adjacent phase which is adjacent to the primary side phase, andwherein the second control mode includes maintaining theprimary-secondary phase difference within the target range and maintainthe secondary side phase between the primary side phase and the primaryside adjacent phase.
 3. The power conversion apparatus according toclaim 2, wherein an intra-primary phase difference between the primaryside phase and the primary side adjacent phase is 120°, and wherein thesecond control mode includes maintaining the primary-secondary phasedifference within the target range which is ±30° of an odd multiple of60°.
 4. The power conversion apparatus according to claim 1, wherein theprimary side phase is a primary side voltage phase of the matrixconverter circuitry, wherein the secondary side phase is a secondaryside current phase of the matrix converter circuitry, and wherein thesecond control mode includes: calculating a deviation between a targetdifference predetermined within the target range and theprimary-secondary phase difference; calculating a voltage command toreduce the deviation; and causing a secondary side voltage of the matrixconverter circuitry to follow the voltage command.
 5. The powerconversion apparatus according to claim 4, wherein the second controlmode includes: generating a target phase of the secondary side voltagephase to maintain the primary-secondary phase difference within thetarget range; and calculating the deviation based on a comparisonbetween the target phase and the secondary side voltage phase.
 6. Thepower conversion apparatus according to claim 5, wherein the secondcontrol mode includes: detecting a current-voltage phase differencebetween the secondary side voltage phase and the secondary side currentphase; and generating the target phase based on the current-voltagephase difference.
 7. The power conversion apparatus according to claim4, wherein the second control mode includes: generating a target phaseso that a target-primary phase difference between the target phase andthe primary side voltage phase is within the target range; andcalculating the deviation based on a comparison between the target phaseand the secondary side current phase.
 8. The power conversion apparatusaccording to claim 4, wherein the second control mode includes:calculating a delay compensation value based on the primary sidefrequency; modifying the phase command value based on the delaycompensation value, so as to compensate for a delay of the deviationreduction; and causing the secondary side voltage phase to follow themodified phase command value.
 9. The power conversion apparatusaccording to claim 8, wherein the second control mode includes repeatinga control cycle comprising: calculating the deviation; calculating thephase command value based on a previous phase command value calculatedin a previous control cycle and the deviation; calculating the delaycompensation value based on the primary side frequency; modifying thephase command value based on the delay compensation value; and causingthe secondary side voltage phase to follow the modified phase commandvalue.
 10. The power conversion apparatus according to claim 9, whereinthe second control mode includes calculating the delay compensationvalue based on the deviation and a cycle time of the control cycle. 11.The power conversion apparatus according to claim 8, wherein the secondcontrol mode includes: calculating the delay compensation valueaccording to a weighted average of the command frequency and the primaryside frequency; and gradually increasing a weight of the primary sidefrequency in the delay compensation value after a shift from the firstcontrol mode to the second control mode.
 12. The power conversionapparatus according to claim 11, wherein the second control modeincludes gradually increasing a weight of the command frequency in thedelay compensation value before a shift from the second control mode tothe first control mode.
 13. The power conversion apparatus according toclaim 2, wherein the second control mode includes causing a secondaryside voltage amplitude of the matrix converter circuitry to follow anamplitude command value different from a primary side voltage amplitudeof the matrix converter circuitry.
 14. The power conversion apparatusaccording to claim 2, wherein the control circuitry is furtherconfigured to: estimate an average heating level based on a secondaryside current of the matrix converter circuitry and a carrier frequency;calculate a concentration coefficient based on a primary-secondaryfrequency difference between the primary side frequency and the commandfrequency; estimate a local heating level based on the average heatinglevel and the concentration coefficient; calculate a deterioration levelbased on the local heating level; and notify that the deteriorationlevel exceeds a predetermined level.
 15. The power conversion apparatusaccording to claim 14, wherein the control circuitry is furtherconfigured to: calculate a deterioration progress based on the localheating level; and integrate the deterioration progress to update thedeterioration level.
 16. The power conversion apparatus according toclaim 15, wherein the control circuitry is further configured to:calculate a temperature rise frequency based on the primary-secondaryfrequency difference; and integrate the deterioration progress at thetemperature rise frequency to update the deterioration level.
 17. Thepower conversion apparatus according to claim 14, wherein the controlcircuitry is further configured to decrease the concentrationcoefficient in response to a shift from the first control mode to thesecond control mode.
 18. The power conversion apparatus according toclaim 14, further comprising a profile storage device that stores acoefficient profile representing a relationship between an absolutevalue of the primary-secondary frequency difference and theconcentration coefficient such that the concentration coefficientincreases as the absolute value of the primary-secondary frequencydifference decreases, wherein the control circuitry is furtherconfigured to calculate the concentration coefficient based on theabsolute value of the primary-secondary frequency difference.
 19. Apower conversion method comprising: selecting a first control mode inresponse to determining that a command-primary frequency differencebetween a command frequency and a primary side frequency of matrixconverter circuitry is above a predetermined threshold, wherein thefirst control mode includes causing a secondary side frequency of thematrix converter circuitry to follow the command frequency; selecting asecond control mode in response to determining that the command-primaryfrequency difference is below the threshold, wherein the second controlmode includes maintaining a primary-secondary phase difference between asecondary side phase and a primary side phase of the matrix convertercircuitry within a predetermined target range; and controlling thematrix converter circuitry in accordance with a selection of the firstcontrol mode or the second control mode.
 20. A non-transitory memorydevice having instructions stored thereon that, in response to executionby a processing device, cause the processing device to performoperations comprising: selecting a first control mode in response todetermining that a command-primary frequency difference between acommand frequency and a primary side frequency of matrix convertercircuitry is above a predetermined threshold, wherein the first controlmode includes causing a secondary side frequency of the matrix convertercircuitry to follow the command frequency; selecting a second controlmode in response to determining that the command-primary frequencydifference is below the threshold, wherein the second control modeincludes maintaining a primary-secondary phase difference between asecondary side phase and a primary side phase of the matrix convertercircuitry within a predetermined target range; and controlling thematrix converter circuitry in accordance with a selection of the firstcontrol mode or the second control mode.